1. Field of the Invention
The present invention relates to a wheel support bearing assembly for rotatably supporting a wheel of, for example, an automotive vehicle and a method of manufacturing such wheel support bearing assembly.
2. Description of the Prior Art
Such a wheel support bearing assembly as shown in FIG. 10 has hitherto been suggested, which is used for rotatably supporting a vehicle drive wheel. See, for example, the Patent Document 1 listed below. The wheel support bearing assembly shown in FIG. 10 includes an outer member 21, an inner member 22 and double rows of rolling elements 25 rollingly interposed between opposed raceway surfaces 23 and 24 defined respectively in the outer member 21 and the inner member 22. The inner member 22 referred to above is made up of a hub unit 29, having a wheel mounting hub flange 29a defined in an outer periphery of the hub unit 29, and an inner ring 30 mounted on an inboard end portion of the outer periphery of the hub unit 29. The hub unit 29 has a center bore 31 defined therein in alignment with the longitudinal axis thereof, and a stem portion 33a of an outer ring 33, forming a part of a constant velocity universal joint, is inserted into the center bore 31 for spline engagement with the hub unit 29, with an annular stepped face 33b of the constant velocity universal joint outer ring 33 then urged against an inboard end face 30a of the inner ring 30. Starting from this condition, when a nut 34, which is threadedly mounted on a free end of the stem portion 33a, is fastened, the inner member 22 can be clamped between the constant velocity universal joint outer ring 33 and the nut 34.
According to the Patent Document 1 referred to above, the inner ring 30 is mounted externally on an inner ring mounting area 35 of a stepped configuration defined in the inboard end portion of the outer periphery of the hub unit 29 so as to be recessed radially inwardly of the hub unit 29; a stepped area 36 is formed in an inboard end of an inner periphery of the inner ring 30; and an inboard extremity 29ba of the hub unit 29 is radially outwardly deformed to form a crimped portion 29b that is then seated within the stepped area 36 in the inner ring 30. In this way, an undesirable separation of the inner ring 30, which would otherwise occur under the influence of an external force generated during assemblage onto the automotive vehicle, is avoided effectively.
[Patent Document 1 ] JP Laid-open Patent Publication No. H09-164803
It has, however, been found that the wheel support bearing assembly of the structure described hereinabove has the following problems:
(1) Because the crimped portion 29b of the hub unit 29 is large in size, the radial step, which defines the stepped area 36 in the inboard end portion of the inner ring 30 as shown in FIG. 11 showing a portion of FIG. 10 on an enlarged scale, is required to have 5 to 7 mm in terms of the difference in radius. Since the radial step of the stepped area 36 is increased in this way, the surface area of the inboard end face 30a of the inner ring 30 decreases, resulting in increase of the contact surface pressure between it and the annular stepped face 33b of the constant velocity universal joint outer ring 33. This in turn constitutes a cause of generation of frictional wear and/or abnormal noises.                (2) If an attempt is made to allow the crimped portion 29b of the hub unit 29 to be accommodated axially inwardly (on an outboard side) of the inboard extremity of the inner ring 30, the stepped area 36 in the inner ring 30 is required to have about 7 to 8 mm in axial length as shown in FIG. 11. Since the axial length of the stepped area 36 increases as discussed above, the inner ring stepped area 36 tends to occupy a position on the line of extension L of the rolling element contact angle θ and a considerable inner ring deformation will occur during the operation under the influence of a load to such an extent as to possibly result in reduction of the longevity. Also, increase of the axial length of the inner ring stepped area 36 results in reduction of the length (surface area) of mounting of the inner ring 30 relative to the hub unit 29 and, accordingly, an inner ring creep may occur, possibly accompanied by reduction in longevity. Those problems may be alleviated if the widthwise (or axial) dimension of the inner ring 30 as a whole is increased, but the increase of the widthwise dimension requires an extra space in a widthwise (or axial) direction.        (3) Also, because the crimped portion 29b of the hub unit 29 is large in size, the crimping punch tends to interfere with the inner ring 30 during the orbital forging to form the crimped portion 29b, resulting in difficulty in processing.        
In order to alleviate the foregoing problems, an attempt has been made to design the stepped area 36 of the inner ring 30 to be shallow enough to be of a depth corresponding to an inner peripheral edge of the inner ring end face 30a as shown in FIG. 12. Even though the stepped area 36 is so designed as to be shallow as discussed above, it has been found that a sufficient proof strength against a separating or pull-out force acting during mounting of the bearing assembly onto the automotive vehicle can be secured. If the crimped portion 29b is employed against the stepped area 36 of such a small size, crimping can be accomplished without relying on the orbital forging. By way of example, the method can be employed, in which as shown in FIG. 13, a bearing assembly is fixed with its inboard side oriented upwardly and, while the bearing assembly is in this condition, a crimping punch 19 of a type having a forefront end outer peripheral surface representing a tapered surface is urged from above into an inner periphery of the inboard end of the hub unit 29 so that the crimped portion 29b of the hub unit 29 can be diametrically expanded over the entire circumference thereof.
With the structure, in which the inboard end portion of the hub unit 29 is crimped to avoid detachment of the inner ring 30 as shown in FIG. 12, the proof strength against the possible separation of the inner ring 30 depends on the amount of augmentation D of the crimped portion 29 in a radially outward direction. In the case of the crimped portion 29b relative to the stepped area 36 of the kind discussed above, the sufficient proof strength against the inner ring separation can be obtained if the amount of augmentation D referred to above, which is normally smaller than the depth of the stepped area 36, is of a value equal to or higher than a predetermined value determined based on the strength calculation and/or the strength test. However, since the stepped area 36, with which the crimped portion 29b is engaged, is shallow, there is the possibility that the proof strength against the inner ring separation would be insufficient if the amount of augmentation D is of a value lower than the predetermined value. Conversely, if the amount of augmentation D is too large, excessive loads will act on various portions of the hub unit 29, except for the crimped portion 29b, and also various portions of the inner ring 30. In view of this, it is desired that the crimping process to form the crimped portion 29b should be carried out in such a way that the amount of augmentation D can be accommodated within a tolerance over the predetermined value referred to above. However, with the crimping process using the crimping punch 19 of the kind discussed above, there is a problem that since the crimped portion 29b cannot be viewed from outside during the processing, it is difficult to ensure the amount of augmentation D that is desired or required.